Health Benefits of Green Tea

In this article, we will see why Dr. Adrew Weil[9] said that if you drink coffee, switch it to tea (see also [38]).

Health Benefits

Some researchers believe green tea may have a protective effect because it contains chemicals known as polyphenols, which have antioxidant properties. The major group of polyphenols in green tea are called catechins, and the most important catechin seems to be epigallocatechin-3-gallate (EGCG).

Some laboratory studies have indicated that green tea may help prevent the growth of certain cancers, including cancer of the skin, lung, breast[19], bladder, liver, prostate[12,20,45], ovarian[23,24], colon, leukaemia[25], colorectal[28] and stomach/esophagus[28]. Test tube studies have suggested that compounds in the tea may help stop new blood vessels from forming, thereby cutting off the supply of blood to cancer cells. It is tempting to think that it would therefore prevent cancer in humans, but results of studies in humans have been mixed. [2]

Most human studies have been observational epidemiological studies in East Asia,[34] in which researchers compared tea drinkers with non-tea drinkers while trying to account for other lifestyle differences. It is difficult to draw firm conclusions from these types of studies.

So, don't let the mixed results prevent you from drinking tea, especially green tea. First of all, green tea is on the list of dietary sources of naturally-occurring antiangiogenic substances studied by Dr. William Li from Angiogenesis Foundation[5].  Other studies[3,15] also suggest that green tea can protect against:
  • Heart disease by reducing blood pressure, cholesterol and blood clotting[16,31,42]
    • Researchers at UCLA found that if you drink at least 3 cups of green or black tea a day, your likelihood of having a stroke drops 21%[7].
  • Diabetes by improving the cells’ response to insulin[17,18]
    • Tea help increase insulin receptivity
  • Alzheimer’s disease and Parkinson’s disease by reducing brain-damaging proteins
    • Both green and black tea hinder the activity of two enzymes in the brain that have been associated with the development of Alzheimer's disease. The effects of green tea were longer lasting—a week—while the effects of black tea lasted only a day.
    • Elderly Japanese men and women who drank only a cup of green tea a day cut their odds of cognitive impairment 38%[7].
    • Lab rats raised on green tea have less damage in the hippocampus, or memory processing region of the brain, and consequently have vastly superior memories and learning abilities in old age[7].
    • Israeli scientists found that EGCG can even revive sick and dying neurons thought lost to degenerative brain disease[7].
    • A new study from the National University of Singapore found a cup of tea a day can keep dementia away. The only requirement was that the tea must be brewed from leaves.[44]
      • The researchers found that regular tea-drinkers lowered their risk of cognitive decline in their later years by 50%.
      • There is even-better news for tea-drinkers who are genetically predisposed to developing Alzheimer’s disease. They could see a reduction in cognitive impairment risk by as much as 86%.
  • Arthritis and osteoporosis by slowing breakdown of cartilage and bone
    • Naturally high in minerals, green tea aids in strong bone density, which is important for maintaining good posture
  • Gastrointestinal disorders by improving liver function
    • An increased consumption of green tea may reduce the risk of liver disease[21].
  • Obesity by increasing metabolism[13,14,37]
    • Oolong tea have been shown to help control body fat by improving the metabolism of nutritional fat
  • Cavities, gum disease and bad breath by destroying bacteria in the mouth
    • Green tea has fluoride in it, making it a superstar for keeping gums and teeth healthy. Green tea can even be used as a mouthwash to maintain breath.
    • Drink your tea in the morning and in moderate amounts.[32,33]
  • Urinary Incontinence[10]
    • Women who drank 4 or more cups of green tea/day were 66% less likely to have incontinence.  However, no similar benefits were found in association with black tea, coffee or oolong tea intake.
  • Infectious Disease[46]
    • For patients with external genital warts, rubbing some green tea ointment on, you can achieve “complete clearance of all warts” in more than 50% of cases.
    • Gargling with green tea may drop the risk of influenza infection seven- or eight-fold, compared to gargling with water, in elderly nursing home residents, where flu can get really serious.

Other Usages

Other things you would like to know about green tea:
  • It's a room deodorizer
    • Green tea leaves have traditionally been used to naturally absorb odors in a room. Place tea leaves in a bowl to help absorb unpleasant odors or leave some in the fridge in place of baking soda.
  • It can soothe skin[22]
    • Spent a little too much time in the sun? Use the naturally calming properties of green tea to soothe sunburned skin. Place green tea in a spray bottle and mist on sunburned areas for all-natural relief. Because it has anti-bacterial qualities, green tea can also be used as an antiseptic to spray on skin blemishes or irritations.
  • It's good for the feet
    • Soaking tired feet in green tea can prevent unpleasant fungal infections.
  • It can help soothe sore throat
    • Try sipping some hot green tea with a spoonful of honey and a dash of red pepper (cayenne) which can soothe the inflamed throat.
  • It can enhance your brain function
    • Green tea contains a naturally occurring amino acid called L-theanine, which has been demonstrated to enhance brain function, improve concentration, calm and reduce anxiety, and improve mood, without sedation or jitteriness.[36]
  • It can help us to keep a good oral health
    • Seven minutes after swishing with green tea, the number of Streptococcus mutans in the plaque scrape from people’s teeth was cut nearly in half.[47]

What to Choose?

All tea (except herbal) comes from the Camellia sinensis plant. Variations in taste are due to where the tea is grown and how it is processed. Once picked, tea leaves start to oxidize, darkening like a sliced apple. Then leaves are heated to halt oxidation. There are different kind of teas based on their oxidization levels. Ordered from most oxidized to least oxidized, we have:

  • Black tea
  • Oolong tea
  • Green tea
  • White tea
Because oxidation destroys catechins, white tea has the highest level of antioxidants while black tea has the lowest. In general, consumption of black tea was not associated with lower risk of cancer[26]

The contents of caffeine also vary depending on the level of oxidation. On the opposite scales, black tea has the highest level of caffeine while white tea has the lowest.  Note that caffeine from tea does not act the same ways as coffee-based caffeine. That’s because tea contains L-Theanine, an amino acid that has a calming effect on the brain. It actually offsets the stimulatory effects of caffeine to supply a steady stream of energy instead of a big rush.[43]

In conclusion, white tea seems to the best because it has the highest antioxidants and lowest caffeine. However, white tea is imported mainly from the Fujian province in China and is only picked once a year, in early spring, which is why it is one of the rarest and most expensive teas. So, in this article, we only focus on green tea.

Among green teas, Cathy Wong's and Dr. Mercola's favorite type is matcha[4,29]:

  • Matcha is made by grinding green tea leaves to a fine powder after they are dried.
  • The miniscule particles make it easier to extract the catechins when we brew the tea, compared to other types of green tea.
  • A University of Colorado study found that matcha has greater potential health effects than other green teas.
    • Matcha had 137 times the amount of EGCG than a popular brand of green tea
  • Researchers at the Fukuoka Institute of Health and Environmental Sciences found that animals fed matcha excreted up to 9 times more PCBs (i.e., detoxification) than a control group.
  • The best Matcha green tea comes from Japan and is steamed, rather than roasted or pan-fried[29].
One study has shown that steeping green or black tea for about five minutes releases more than 80% of its catechins into the water. Note that instant iced tea contains almost no catechins. Brew using water that is not quite boiling (160-180°F or 70-80°C). Steep for about 3-5 minutes to avoid bitterness, using a covered glass or ceramic cup . Strain loose leaves before drinking.  Most tea may be infused 3 or more times.

The larger the leaf fragments, the higher the antioxidant content — so choose loose tea with recognizable leaf tips, such as the
Sencha variety from Japan. Tea bags are convenient but contain smaller fragments and lower antioxidant. To avoid possible contamination with lead, pesticides or other toxins, opt for organic teas.  The reason?  Unlike a tomato or an apple, tea cannot even be washed after harvesting. Water initiates the oxidation process, which turns green tea into black or oolong tea, and also develops 
caffeine and other enzymes. Water would ruin the colors and integrity of tiny fragile herbs. The bottom line then, is that whatever has been sprayed on the leaves or worked into the soil, brews directly into the cup. So, that's reason why you should opt for organic teas.

Antioxidants degrade over time, so buy only as much green tea as you can use within six months. Choose light-colored loose leaves with no moldy scent. Store tea leaves and bags in an airtight, opaque container along with a desiccant packet. Place in a cool, dry place or refrigerate.

An animal study suggests that eating black pepper at the same time as drinking green tea can significantly increase the amount of the EGCG absorbed by your body. Citrus juice may also increase catechins’ absorption from the digestive tract, so add lemon if you like. However, do not add milk — its proteins may decrease catechin absorption. Herbal or fruit flavoring does not affect antioxidant levels. From the perspective of antiangiogenic potency, Dr. William Li has found that if you combine two less potent teas (i.e., in this case, he's blended
Chinese Jasmine with Sencha) together, the blend is more potent than either one alone[6].  This means that there is food synergy.

If you prefer decaffeinated tea, check labels and choose a brand that uses the catechin-sparing carbon dioxide method of decaffeination, not the
ethyl acetate method. 

Possible Problems or Complications

Green tea is generally considered safe. A daily cup or two of green tea is not known to be at all harmful. However, some people may develop allergic reactions to the tea, and they should stop drinking it. In addition, there have been increasing reports of acute (but reversible) liver failure among people who took green tea extracts. A laboratory study also suggests that daily megadoses of EGCG may promote tumor growth. These cases suggest that people should drink the tea rather than take green tea supplements.

Check with your doctor first if you take blood-thinning medication, such as
warfarin (Coumadin). Drinking large amounts of green tea—a half gallon to a full gallon a day—could reduce the effectiveness of these drugs.  
Individuals who take nadolol should be aware of its potential interaction with green tea as reported in [35] and should discuss this with their physician too.

In addition, drinking large amounts of tea may cause nutritional and other problems. Green tea contains caffeine, and high doses of caffeine can contribute to many health problems[1]. The tannins in tea may reduce the body's absorption of iron. Individuals with cancer who are having problems with eating and maintaining weight might need to replace tea with higher-calorie liquids.


  1. If You Drink Too Much Caffeine
  2. Complete Guide to Nutrition for Cancer Survivors by Barbara L. Grant, Abby S. Bloch, Kathryn K. Hamilton, Cynthia A. Thomson.
  3. The Healthy Connoisseur's Guide to Green Tea by Lester A. Mitscher, PhD
  4. This Inside Out Diet by Cathy Wong, N.D. C.N.S.
  5. Naturally-Occurring Antiangiogenic Substances
  6. Eat to fight cancer(video)
  7. 100 Simple Things You can Do to Prevent Alzheimer's by Jean Carper
  8. How to Live Longer and Healthy Life
  9. Spontaneous Happiness by Andrew Weil, MD
  10. Urinary Incontinence Alternatives
  11. Green Tea (
  12. Bettuzzi S, Brausi M, Rizzi F, Castagnetti G, Peracchia G, Corti A. Chemoprevention of human prostate cancer by oral administration of green tea catechins in volunteers with high-grade prostate intraepithelial neoplasia: a preliminary report from a one-year proof-of-principle study. Cancer Res. 2006;66(2):1234-40.
  13. Boschmann M, Thielecke F. The effects of epigallocatechin-3-gallate on thermogenesis and fat oxidation in obese men: a pilot study. J Am Coll Nutr. 2007;26(4):389S-395S.
  14. Brown AL, Lane J, Holyoak C, Nicol B, Mayes AE, Dadd T. Health effects of green tea catechins in overweight and obese men: a randomised controlled cross-over trial. Br J Nutr. 2011 Jun 7:1-10.
  15. Cooper R, Morre DJ, Morre DM. Medicinal benefits of green tea: Part I. Review of noncancer health benefits. J Altern Complement Med. 2005;11(3):521-8.
  16. Fujita H, Yamagami T. Antihypercholesterolemic effect of Chinese black tea extract in human subjects with borderline hypercholesterolemia. Nutr Res. 2008;28(7):450-6.
  17. Fukino Y, Ikeda A, Maruyama K, Aoki N, Okubo T, Iso H. Randomized controlled trial for an effect of green tea-extract powder supplementation on glucose abnormalities. Eur J Clin Nutr. 2007.
  18. Hsu CH, Liao YL, Lin SC, Tsai TH, Huang CJ, Chou P. Does supplementation with green tea extract improve insulin resistance in obese type 2 diabetics? A randomized, double-blind, and placebo-controlled clinical trial. Altern Med Rev. 2011 Jun;16(2):157-63.
  19. Inoue M, Tajima K, Mizutani M, et al. Regular consumption of green tea and the risk of breast cancer recurrence: follow-up study from the Hospital-based Epidemiologic Research Program at Aichi Cancer Center (HERPACC), Japan. Cancer Lett. 2001;167(2):175-182.
  20. Jian L, Xie LP, Lee AH, Binns CW. Protective effect of green tea against prostate cancer: a case-control study in southeast China. Int J Cancer Jan 1, 2004;108(1):130-135.
  21. Jin X, Zheng RH, Li YM. Green tea consumption and liver disease: a systematic review. Liver Int. 2008;28(7):990-6.
  22. Katiyar SK, Ahmad N, Mukhtar H. Green tea and skin. Arch Dermatol. 2000;136(8):989-94.
  23. Zhang M, Lee AH, Binns CW, Xie X. Green tea consumption enhances survival of epithelial ovarian cancer. Int J Cancer Nov 10, 2004;112(3):465-469.
  24. Zhou B, Yang L, Wang L, Shi Y, Zhu H, Tang N, Wang B. The association of tea consumption with ovarian cancer risk: a meta-analysis. Am J Obstet Gynecol. 2007;197(6):594.e1-6.
  25. Zhang M, Zhao X, Zhang X, Holman CD. Possible protective effect of green tea intake on risk of adult leukaemia. Br J Cancer. 2008;98:168–70. 
  26. Tea and Cancer Prevention: Epidemiological Studies
  27. Does drinking tea produce a diuretic effect?
    • Single servings of caffeine at doses exceeding 300mg may have a diuretic effect. But, a tolerance to caffeine develops so any diuretic effect is diminished in people who regularly drink tea.
  28. Prospective cohort study of tea consumption and risk of digestive system cancers: results from the Shanghai Women's Health Study.  Am J Clin Nutr. 2012 Nov;96(5):1056-63. doi: 10.3945/ajcn.111.031419. Epub 2012 Oct 10.
  29. Potent “Superfoods” That Can Improve Your Health and Increase Longevity
  30. Green Tea (Univ. of Maryland Medical Center)
  31. Nagaya N, Yamamoto H, Uematsu M, Itoh T, Nakagawa K, Miyazawa T, Kangawa K, Miyatake K : Green tea reverses endothelial dysfunction in healthy smokers. Heart, 90: 1485-1486, 2004. 
    • Research results suggest that green tea consumption reverses endothelial dysfunction in healthy smokers, possibly through its antioxidant effect. 
    • Research results also suggest that green tea may act as a potent antioxidant.
      • Compared with black tea, green tea contained extremely large amounts of catechins including epigallocatechin gallate.
      • Unlike black tea, green tea contained ascorbic acid, which also has antioxidant effects. 
  32. Health Effects of Element Fluorine (F) (Travel to Health)
    • Be warned that chronic excess fluoride consumption can lead to skeletal fluorosis.
    • In Tibet, excessive consumption of poor-quality pu-erh tea is reported to cause fluorosis.
  33. If You Drink Too Much Caffeine (Travel and Health)
  34. Coffee, Decaffeinated Coffee, Caffeine, and Tea Consumption in Young Adulthood and Atherosclerosis Later in Life: The CARDIA Study
  35. Green tea may interfere with a blood pressure medicine
  36. Anti-stress effect of theanine on students during pharmacy practice: positive correlation among salivary α-amylase activity, trait anxiety and subjective stress.
  37. Green tea catechin consumption enhances exercise-induced abdominal fat loss in overweight and obese adults.
  38. Sodas, Tea and Coffee: Which Can Lower Your Bone Density?
    • Drinking coffee, but not tea, could lead to osteoporosis in women
  39. 《茶,一片树叶的故事》 第一集 土地和手掌的温度 (in Chinese)
  40. 《茶,一片树叶的故事》 第四集 他乡,故乡 (in Chinese)
  41. The ancient fat-burning tea you need to start drinking
    • Pu-erh is different than most teas, as it undergoes a natural fermentation process and is aged like a fine wine.
  42. The Protective Effect of Habitual Tea Consumption on Hypertension
  43. Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses
    • The findings suggest that L-theanine not only reduces anxiety but also attenuates the blood-pressure increase in high-stress-response adults
  44. Tea consumption reduces the incidence of neurocognitive disorders: Findings from the Singapore longitudinal aging study. The Journal of Nutrition, Health & Aging, 2016; 20 (10)
  45. Treating Prostate Cancer with Green Tea (video)
  46. Benefits of Green Tea for Boosting Antiviral Immune Function
  47. What’s the Best Mouthwash?
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